Deniro? Maybe, but in my opinion he either plays gangster or some dumb guy in comedy movies, and he acts all the same.
I watched only There will be blood and Gangs of New York and his acting was very very decent, especially in there will be blood, one of the few times when I can't say for sure whether I love this character or not.
Leo, heh, i can't say for sure. it's like choosing between Zywoo or S1mple, both are great, but perhaps my bias influenced this moment